Conventionally, there is one using a rotary damper with an object for slowly activating a door and the like urged in one side of an open direction or a closing direction. The rotary damper comprises a damper housing internally enclosing a viscous fluid; and a rotor including a rotor vane received in the damper housing, and a rotor axis provided to project in the rotor vane and protruding from the damper housing. The rotary damper is combined with the rotary member such as the gear and the like to damp the rotation in the rotor axis. Such rotary damper is sometimes used in combination with a one-way clutch to generate a damping force relative to only a unidirectional rotation (for example, Patent Document 1).